The use of elemental fluorine for the site specific fluorination of aliphatic compounds is rarely satisfactory due to the high reactivity of the element which leads to unspecific multiple substitution, carbon-carbon bond cleavage and oxidation. Because of the growing importance of fluorinated organic compounds in applications such as in biochemical systems, (Ref 1: R Filler, Y Kobayashi (editors); Biomedical Aspects of Fluorine Chemistry; Elsevier Biomedicinal Press, New York, 1982), (Ref 2: J T Welch; Tetrahedron, 1987, 43, (14), 3123) in recent years considerable effort has gone into finding ways of introducing fluorine into specific sites within molecules to provide building blocks for the preparation of biologically active compounds which have more complex structures. In this context, the replacement of the 2 hydrogen in 1,3-diketones and 1,3-ketoesters is just one transformation that has aroused much interest since the mono- and/or di-fluorinated products can be useful intermediates in the preparation of bio-active molecules. This transformation has been carried out either by treating the 1,3-diketone or 1,3-ketoester or their metal enolates with one of several "electrophilic fluorinating agents" that have been developed recently. For example, 1,3-diketones and 1,3-ketoesters have been treated with acetyl hypofluorite (Ref 3: S Rozen and O Lerman; J. Org. Chem., 1983, 48, 724), N-fluoro-pyridinium salts with or without a Lewis Acid catalyst (Ref 4: T Umemoto et al; J Amer. Chem. Soc., 1990, 112, 8563), xenon difluoride (Ref 5: B Zajc and M Zupan; J Chem Soc., Chem Commun, 1980, 759), lamellar C.sub.19 XeF.sub.6 (Ref 6: H B Kagan, S S Yemul and R Setton; Tetrahedron Letts., 1980, 21, 277), and N-fluorobis[(perfluoroalkyl)sulphonyl]imides (Ref 7: G Resnati and D D Desmarteau; J Org. Chem., 1992, 57, 4281) (Ref 8: Z Xu, D D Desmarteau and Y Gotoh; J Fluorine Chem., 1992, 58, 71), (Ref 9: G Resnatti and D D Desmarteau; J. Org. Chem., 1991 56, 4925), (Ref 10 Z Xu, D D Desmarteau and Y Gotoh; J Chem Soc; Chem. Commun; 1991, 179) and their metal enolates have been treated with acetyl hypofluorite (Ref 3), N-fluoro-pyridinium salts (Ref 4).
Thus, although the treatment of 1,3-diketones and 1,3-ketoesters with electrophilic fluorinating agents can sometimes give high yields of the required mono- or di-fluorinated products, some of these reagents decompose fairly quickly, and the compounds from which they are made are often expensive or difficult to obtain.